|Publication number||US7224155 B2|
|Application number||US 10/888,790|
|Publication date||May 29, 2007|
|Filing date||Jul 9, 2004|
|Priority date||Jul 10, 2003|
|Also published as||CN1839359A, US20050007189, US20050035749|
|Publication number||10888790, 888790, US 7224155 B2, US 7224155B2, US-B2-7224155, US7224155 B2, US7224155B2|
|Inventors||Gian Marco Bo, Massimo Mazzucco|
|Original Assignee||Atmel Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Referenced by (11), Classifications (9), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims priority to Italian Application Serial Number TO2003A000533, filed Jul. 10, 2003.
1. Field of the Invention
The invention relates generally to voltage regulators and specifically to limiting the short circuit current in a voltage regulation circuit.
2. The Prior Art
Amplifier 30 compares the voltage across resistor 40 with reference voltage Vbg. Output voltage Vout is determined by the combination of reference voltage Vbg and resistors 35 and 40. As current IL increases above its maximum level, amplifier 30 starts to work in a non-liner mode (i.e. saturation) and as a consequence there is a decline the output voltage Vout. The voltage versus current behavior depends on the characteristics of transistor 15. One problem with circuit 10 is that if transistor 10 is large (for example, in order to have good power supply rejection ratio), then amplifier 30 saturates for high values of current IL in a regulator that features low current load range. This means that the regulator presents a very high short circuit current compared to the typical regulator load current. Such short circuit current primarily depends on characteristics of transistor 15 and is not directly controllable.
One solution for the above referenced problem features a switch connected between the gate of transistor 15 and the supply voltage 20, and controlled by the load current value IL. When the current IL is lower than a predetermined threshold the switch is open and the regulator works in normal operation. When IL is higher than the threshold, the switch is closed thus fixing the voltage at the controlling node of transistor 15, and so limiting the short circuit current of the regulator at the selected current threshold. The problem with this approach is that the rapid on-off state sequencing of the switch causes oscillation in circuit behavior.
What is needed is a current limitation circuit based on a simple architecture that provides a predictable output response and does not alter the behavior of the regulator in normal operation.
A circuit for limiting a power current from a power-controlling pass device, the power-controlling pass device being coupled to a supply voltage, comprises the following. A sense device is coupled to the supply voltage with the sense device being configured to draw a sense current that is proportional to the power current. A current mirror is coupled to the sense device and the supply voltage through a low impedance node, for example a resistor, the current mirror being configured to draw a mirror current through the low impedance node that is relative to the sense current. In one embodiment the mirror current is approximately equal to the sense current, and therefore has approximately the same proportion to the power current. A limiting device is coupled to the supply voltage, the power-controlling pass device, and the low impedance node, the limiting device being configured to limit the power current according to a voltage difference between the low impedance node and the supply voltage. In one embodiment the limiting device, the power-controlling pass device and the sense device are all MOS transistors.
The following description the invention is not intended to limit the scope of the invention to these embodiments, but rather to enable any person skilled in the art to make and use the invention.
The sense device should provide a current based on the current of the device it is sensing. In this embodiment, sense device, or transistor 110, is smaller than transistor 15 by a known ratio and therefore provides a current through itself with the known ratio to the current through transistor 15. Current through transistor 110 necessarily passes through current mirror 120 and transistor 135 to ground. Current through node 150 and into current mirror 120 reflects, or approximates, current through transistor 110. Current mirrors may provide whatever ratio of current is desired, but in this embodiment a one-to-one ratio is used. Current through node 150 approximates the current through transistor 15 by the ratio of transistor 110 to transistor 15. If K is the ratio of transistor 110 to transistor 15 and current through transistor 15 is Il (neglecting current through resistors 35 and 40), then current through node 150 is KˇIl.
In one embodiment, resistor 140 couples to supply voltage 20 and converts KˇIl into a voltage across the source and gate of transistor 160. Limiting device, or transistor 160, clamps the voltage at the gates of transistors 110 and 15. Transistor 160 is driven through its gate by the voltage across resistor 140 with a resistance of Rlm, for a gate voltage of RlmˇKˇIl. In one embodiment transistor 160 is a PMOS transistor.
Transistor 160 is driven by a low impedance node and may operate in saturation, so the transition between normal operation and an overcurrent mode is continuous and no stability problems appear since no on-off state sequence of transistor 160 occurs.
where Vs is the saturation voltage of amplifier 30, Av is the DC differential voltage gain of amplifier 30, Vdd is supply voltage 20, V+ is the noninverting input to amplifier 30, and V− is the inverting input to amplifier 30.
Vg is the gate voltage of transistors 110 and 15. Vg is determined by amplifier 30 and transistor 160:
Ilm is the drain current of transistor 160 that is, when transistor 160 is on and in saturation:
where Vtop is the threshold voltage and βlm is the gain factor of transistor 160. So
Current limitation circuit 100 has three modes of operation: normal, overcurrent and short circuit. In normal operation, load current Il increases from zero and the regulation loop (transistor 15, resistors 35 and 40, and amplifier 30) makes Vout stable by adapting (i.e., by reducing) voltage Vopa. Once Il increases to where RlmˇKˇIl>|Vtop| (the threshold voltage of transistor 160), transistor 160 turns on and begins injecting current Ilm into the output of amplifier 30 and so modifying voltage Vg (the gate voltage of transistors 110 and 15). While amplifier 30 is in the linear region, voltage Vopa is adapted to compensate the effect of Ilm and Vout remains stable. In normal operation transistor 15 is in the triode region and amplifier 30 is in the linear region, so:
βreg is the gain factor of transistor 15, R1 is the resistance of resistor 35 and R2 is the resistance of resistor 40. Substituting, the equation for Vg into the equation for Il,
So, solving the quadratic equation for Vout:
This is valid while amplifier 30 is in the linear region, i.e.,
As Il increases, Vopa decreases until it reaches Vs and amplifier 30 leaves the linear region and current limitation circuit 100 goes into overcurrent operation. The transition from normal to overcurrent operation is continuous and stable because a low impedance node (resistor 140) drives transistor 160 and transistor 160 is in saturation when reaching the saturation voltage of amplifier 30. The regulation loop does not work and voltage Vg becomes
As Il increases, the drain-to-source voltage of transistor 15 increases, and Vout starts to decrease. Due to current limitation circuit 100, Vg (gate voltage for transistors 110 and 15) is limited not to Vs (saturation voltage of amplifier 30), which occurs when no current limitation is present, but to a higher value, so the output voltage Vout begins decreasing at a lower level of load current Il.
During overcurrent operation, the current in transistor 15 is
Substituting, for Vg yields
Solving for Vout:
This is valid while transistor 15 is in the triode region,
As Il increases, Vout decreases and transistor 15 exits the triode region and enters saturation. Current limitation circuit 100 now enters short circuit operation. Load current Il is, while neglecting the channel modulation in transistor 15,
Substituting for Vg yields:
and Vout goes to zero.
This value for load current Il represents the short circuit current, i.e., the current flowing in transistor 15 when Vout is zero (note that FIL is a function of Il, so the equation must be solved numerically). The short circuit current can be programmed by choosing the value of K, Rlm, and the size of transistor 160.
Without current limitation circuit 100, the short circuit current is
which is higher than the short circuit current with current limitation circuit 100.
The preceding equations apply to one exemplary embodiment and are not meant to limit the invention. The equations are presented in order to assist in understanding one embodiment of the invention. Any person skilled in the art will recognize from the previous description and from the figures and claims that modifications and changes can be made to the invention without departing from the scope of the invention defined in the following claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4593338||May 4, 1984||Jun 3, 1986||Mitsubishi Denki Kabushiki Kaisha||Constant-voltage power supply circuit|
|US4605891||Jun 21, 1984||Aug 12, 1986||Motorola||Safe operating area circuit and method for an output switching device|
|US4771228 *||Jun 5, 1987||Sep 13, 1988||Vtc Incorporated||Output stage current limit circuit|
|US4851953||Oct 28, 1987||Jul 25, 1989||Linear Technology Corporation||Low voltage current limit loop|
|US5570060||Mar 28, 1995||Oct 29, 1996||Sgs-Thomson Microelectronics, Inc.||Circuit for limiting the current in a power transistor|
|US5614850||Dec 9, 1994||Mar 25, 1997||Texas Instruments Incorporated||Current sensing circuit and method|
|US5789971||Nov 17, 1995||Aug 4, 1998||Co.Ri.M.Me.-Consorzio Per La Ricerca Sulla Microeletrronica Nel Mezzogiorno||Protection circuit and method for power transistors, voltage regulator using the same|
|US5955915||Feb 13, 1996||Sep 21, 1999||Stmicroelectronics, Inc.||Circuit for limiting the current in a power transistor|
|US6304108||Jul 14, 2000||Oct 16, 2001||Micrel, Incorporated||Reference-corrected ratiometric MOS current sensing circuit|
|US6396311||Jul 30, 2001||May 28, 2002||Micrel, Incorporated||Transconductance amplifier circuit|
|US6407537||Dec 19, 2000||Jun 18, 2002||Koninklijke Philips Electronics N.V.||Voltage regulator provided with a current limiter|
|US6476667||Oct 24, 1997||Nov 5, 2002||Texas Instruments Incorporated||Adjustable current limiting/sensing circuitry and method|
|US6480043||May 24, 1999||Nov 12, 2002||Semiconductor Components Industries Llc||Circuit and method for protecting a switching power supply from a fault condition|
|US6522111 *||Aug 28, 2001||Feb 18, 2003||Linfinity Microelectronics||Linear voltage regulator using adaptive biasing|
|US6580257||Sep 24, 2002||Jun 17, 2003||Stmicroelectronics S.A.||Voltage regulator incorporating a stabilization resistor and a circuit for limiting the output current|
|US6801419||Jun 21, 2002||Oct 5, 2004||Seiko Instruments Inc.||Overcurrent protection circuit for voltage regulator|
|US6804102||Jan 18, 2002||Oct 12, 2004||Stmicroelectronics S.A.||Voltage regulator protected against short-circuits by current limiter responsive to output voltage|
|US6861832 *||Jun 2, 2003||Mar 1, 2005||Texas Instruments Incorporated||Threshold voltage adjustment for MOS devices|
|US7005924 *||Jul 8, 2004||Feb 28, 2006||Intersil Americas Inc.||Current limiting circuit with rapid response feedback loop|
|US20020005738||Jul 30, 2001||Jan 17, 2002||Inn Bruce Lee||Transconductance amplifier circuit|
|US20040051508||Dec 28, 2001||Mar 18, 2004||Cecile Hamon||Voltage regulator with enhanced stability|
|USRE37778||Apr 30, 2001||Jul 2, 2002||Siemens Aktiengesellschaft||Current limiting circuit|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7813096 *||Dec 26, 2006||Oct 12, 2010||Autonetworks Technologies, Ltd.||Power supply controller|
|US8305066 *||May 24, 2010||Nov 6, 2012||Industrial Technology Research Institute||Low dropout regulator|
|US8416547 *||Nov 29, 2006||Apr 9, 2013||National Semiconductor Corporation||Short circuit protection with reduced offset voltage|
|US8760132 *||Jun 24, 2010||Jun 24, 2014||Stmicroelectronics (Research & Development) Limited||Supply voltage independent quick recovery regulator clamp|
|US8884594 *||Feb 13, 2012||Nov 11, 2014||Seiko Instruments Inc.||Voltage regulator|
|US20080123235 *||Nov 29, 2006||May 29, 2008||Kwok-Fu Chiu||Short circuit protection with reduced offset voltage|
|US20100134939 *||Dec 26, 2006||Jun 3, 2010||Autonetworks Technologies, Ltd||Power supply contoller|
|US20100327840 *||Jun 24, 2010||Dec 30, 2010||Stmicroelectronics (Research & Development) Limited||Supply voltage independent quick recovery regulator clamp|
|US20110050197 *||Jul 20, 2010||Mar 3, 2011||Nec Electronics Corporation||Reference current or voltage generation circuit|
|US20110156674 *||May 24, 2010||Jun 30, 2011||Industrial Technology Research Institute||Low dropout regulator|
|US20120206119 *||Feb 13, 2012||Aug 16, 2012||Masakazu Sugiura||Voltage regulator|
|U.S. Classification||323/312, 323/315|
|International Classification||G05F3/16, G05F1/573, G05F3/26|
|Cooperative Classification||G05F1/573, G05F3/262|
|European Classification||G05F3/26A, G05F1/573|
|May 11, 2005||AS||Assignment|
Owner name: ATMEL CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BO, GIAN MARCO;MAZZUCCO, MASSIMO;REEL/FRAME:016563/0800
Effective date: 20040527
|Nov 29, 2010||FPAY||Fee payment|
Year of fee payment: 4
|Jan 3, 2014||AS||Assignment|
Owner name: MORGAN STANLEY SENIOR FUNDING, INC. AS ADMINISTRAT
Free format text: PATENT SECURITY AGREEMENT;ASSIGNOR:ATMEL CORPORATION;REEL/FRAME:031912/0173
Effective date: 20131206
|Oct 29, 2014||FPAY||Fee payment|
Year of fee payment: 8
|Apr 7, 2016||AS||Assignment|
Owner name: ATMEL CORPORATION, CALIFORNIA
Free format text: TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENT COLLATERAL;ASSIGNOR:MORGAN STANLEY SENIOR FUNDING, INC.;REEL/FRAME:038376/0001
Effective date: 20160404